The present invention relates to a semiconductor device that has a plurality of substrates and a method for fabricating the device.
Lately, the present inventor has proposed this kind of semiconductor device obtained by laminating a conductive layer and an insulating layer on a first semiconductor substrate, polishing its surface by chemical mechanical polishing (hereinafter abbreviated to CMP) for the formation of a flat first bonding surface on which a silicon nitride film that serves as an insulating layer and copper that is a through hole conductor for plugging a through hole of the silicon nitride film are exposed, laminating a conductive layer and an insulating layer on a second semiconductor substrate, subjecting its surface to CMP for the formation of a flat second bonding surface on which a silicon nitride film and copper that is a through hole conductor are exposed, further applying pressure welding loads to the first semiconductor substrate and the second semiconductor substrate for the achievement of the solid state bonding of the first bonding surface to the second bonding surface and electrically connecting the through hole conductors to each other. It is to be noted that this semiconductor device is mentioned for the sake of explaining the present invention, and this means that the device has not vet been made public and is not the prior art.
This semiconductor device has the advantages that it can simply prevent electromagnetic radiation noises because of the provision of the conductive layer on the first and second substrates and that the interconnections can be made short and easy because the through hole conductors are bonded together in the solid state bonding manner.
However, the aforementioned semiconductor device, in which the through hole conductors that are made of copper and provided inside the through holes of the silicon nitride films have a hardness lower than that of the silicon nitride films that are the insulating layers. Therefore, when the first bonding surface and the second bonding surface are subjected to CMP, then dishing (a dish-shaped hollow) occurs on the surface of the through hole conductors, and this possibly leads to a fail in directly bonding the through hole conductors to each other. That is, the electrical connection of the through hole conductors has no reliability.